May 30, 2011

Panspermia is the notion that microbes can stowaway on space debris and ride a comet or meteorite from one environment to the next, seeding new areas with biology. This concept started out as merely curiosity among astrobiologists, but our understanding of panspermia has changed since the discovery of some unusual meteorites from Mars. The first these peculiar rock is the so-called Murchison meteorite that landed in Australia over 50 years ago. Scientists studying the rock found amino acids within the rock, the first evidence suggesting an extraterrestrial origin for some of life’s ingredients. Later on, a Martian meteorite found in Allan Hills, Antarctica catalogued as ALH84001 sparked controversy again when scientists believed that micro crystals of iron and carbon suggested remnants of life; since then, most of academia refutes these claims, but the possibility that microbes can hitch rides on satellites is still a very real possibility.

How likely is it that germs could survive a trip from Earth to Mars? Research suggests that this journey could take 100 million years one-way and that some forms of life can wait out that long period and be revived later. We know certainly that our biology can survive that time if properly shielded from the heat of entry and re-entry and the deadly radiation that would bombard it in transit. If a germ were protected by a thin layer of rock, it could ride out the journey from one world to the next with little problem. Germs can form spores that all but shut down their metabolism, leaving them inert for a while until the right environmental conditions start them up again. Not only single-celled organisms, but tardigrades, the so-called water bears can suspend their metabolism in a state of cryptobiosis until conditions are better for their survival. Not only can water bears induce a form of suspended animation, they can survive in near boiling temperatures, well below freezing, and can withstand over 1,000 times the amount of radiation that a human can endure. Water bears could be the most resilient animals on Earth. It’s certainly conceivable that his durable bug could be a pioneer on Mars, living in such a bleak environment as a Martian desert.

Could life have arisen on Mars when it was more habitable? And if so, could it have traveled to Earth? While Mars today is dry and barren, long ago it could have been habitable to life as we know it.

When NASA scientists cracked open an Surveyor 3 spacecraft after its sojourn in space, they found bacteria that had survived the vacuum of space for 3 years; the brutal environment of outer space didn’t kill that hearty germ, and so scientists began to talk about the idea of backward contamination. When the Apollo team first went up into space, NASA scientists were deeply concerned that the Moon might harbor viruses or germs that the Earthmen would have no immunity to; when their physicals came back clean, only then were they allowed out of quarantine. Since then, we know that the moon is very unlikely to harbor any kind of life, but the discovery that germs can ride out the vacuum of space leaves many researchers concerned that in the future, probes bound for potentially habitable abodes might contain Earth-borne germs that could colonize these exotic worlds and we could inadvertently spread life to the outer reaches of the solar system. The concern arises however, if we ever discover life out in our solar system; would our discover hail a genuine second origin, or are we just “rediscovering” Earth-life that relocated to a new habitat after we unwittingly contaminated a world with our germs? NASA has since taken huge precautions towards preventing both forward contamination of our research sites on Mars and beyond and backward contamination of any “Andromeda strain” of bacteria that we happen to take back to Earth with us.

What about deliberate panspermia? So far, the discussion has been about mistakenly spreading life, but what if we chose to deliberately seed the cosmos with our own biology? In the future, humans could build probes that would fly to other stars, carrying a payload of ready-made life that could set up shop on distant habitable planets. Our descendants could be fruitful and multiply throughout the universe in a scheme to colonize the universe like a celestial honey bee that pollinates across a vast field of stars.

May 22, 2011

Check out this press release from Astrobiology Magazine on a recent discovery by scientists associated with NASA’s Jet Propulsion Labratory. Up to 10 Jupiter-sized planets have been found wandering the galaxy, completely free of an orbiting star. This new discovery will improve our understanding of how solar systems develop.

One can only imagine what the sky would look like from this planet with the perpetual twilight of a forever-evolving backdrop of stars.

May 18, 2011

Extremophiles are organisms on Earth that can tolerate boiling temperatures, freezing cold, crushing deep-sea pressures, toxic environments or deadly radiation. Creatures like tardigrades, the so-called water bears, can survive grueling conditions for human beings with no harm. In a process called panspermia, life or its precursor can be spread across vast distances by comet and meteorite impacts on planetary bodies.

During cataclysmic events like a volcanic eruption or a meteorite impact, these extremophiles can get sent into the upper atmosphere on a hunk of rock and even get launched into outer space. If these creatures were encased in a layer of rock sufficiently think enough to keep them protected by the harsh radiation and cold vacuum of space, some might be able to encapsulate themselves in a spore and ride out an excursion through our inner solar system. Some bacteria and even animals can form dehydrated spores that leave them in a state of suspended animation called cryptobiosis; cryptpbiosis is a metabolic state that resembles death, but when conditions become more favorable to these organisms in stasis, they revive themselves and come back to life, so to speak. Extremophiles are of interest to us as astrobiologists because such organisms could potentially survive a transit from one planetary body in our solar system to another. Any stowaway microbes from our world that hitch a ride on a meteor or asteroid could potentially survive the impact on another planet like Mars and colonize that planet if conditions.
Some speculate that it may even be possible to send a bacterium across the stars from one solar system into another, but the odds of that would be significantly lower than a transit within a solar system. However, astrochemistry can produce complex organic molecules like benzene and even ribose sugar. These chemicals are the precursors to life and their creation in such a hostile environment like space may mean that life is common in the universe. And if these chemicals could be made in space, then panspermia would send these building blocks down onto a suitable planet. Some scientists speculate that water was brought to Earth via comet impacts after the formation of the Earth. An analysis of the water on Earth shows that the hydrogen in water is sometimes made of a heavier deuterium isotope. Based off of this analysis, researchers have suggested that the water delivered to Earth from space only contributed a modest amount when compared to the amount out-gassed through the crust during the formation of the Earth. On Areios, water brought by comets plays even less of a role in the amount of water on the planet. Because of Areios’ larger mantle and greater mass, more water gets outgassed from the crust and that water gets held in the atmosphere for longer because there is more gravity on Areios to hold it down.
Then there’s the issue of directed panspermia of life; could an intelligent race seed the universe with life? There is a concept known as the Fermi paradox which asks that if the universe is about 14 billion years old and even if an alien civilization could traverse our galaxy at a rate of 1/1000 the speed of light, then it could take an alien civilization 100 million years to colonize the galaxy. This means that in the span of the age of our galaxy, an intelligent species could have conquered our galaxy 140 times in that window. Of course, the earliest civilizations couldn’t have formed until terrestrial planets formed, but even if the first intelligent species didn’t get started until 10 billion years ago, that’s still 100 times the duration a species would need to colonize a whole galaxy. Fermi then wondered; what was holding a species back? Maybe colonization is impossible. If we can travel the universe in warp-powered star-ships, then maybe we can send unmanned probes as our emissaries to the starts. Locked safely away in our far-flung satellites, we could include some freeze-dried samples of extremophiles. Our probes wouldn’t seek out new life and new civilizations, but would rather look for uninhabited planets capable of sustaining life to drop their payload of ready-made bacteria to get a new colony of earth life ready.

Even moving at a fraction of the speed of light, a spacefaring civilization should have been able to colonize our galaxy by now. Where are they?

May 13, 2011

The shadow biosphere is the concept that in between the formation of the planet and the earliest-known undisputed evidence of life on Earth, there could have potentially have been more than one genesis. Stanley Miller of the Urey-Miller experiment (which proffered that amino acids could be made from non-living chemical reactions) suggested that chemical evolution could take on the order of magnitude of around 20-100 million years. But the Earth’s crust cooled around 4.5-4.3 billion years ago and the earliest fossils may date to around 3.5 billion years ago (with some sketchier evidence suggesting it was as early as 3.8 billion years ago) This means that in between the formation of the Earth and the formation life, there is a gap of half a billion to a billion years where life could have potentially arisen. And if life could take even a conservative 100 million years to form, then there could have been up to five genesis events between 4.3 and 3.8 billion years ago, or radically, there may have even been up 50 possible events. Could life from an earlier iteration have survived into the present day? How would we know? All life on Earth shares the same characteristics and we can study molecular clues to determine levels of relatedness between species. Researchers found that all life must have had a last universal common ancestor, most likely a single-celled archean life called a thermohalophile, a creature that could have survived in acidic, boiling water. The adaptations this creature used enabled it to thrive and multiply, creating ever more complex progeny through the slow process of evolution.

All amino acids (the building blocks of proteins) on Earth are right-handed and all nucleic acids (the building blocks of DNA) are left-handed. If we found a life form that differed, it would be completely unlike anything on Earth. Scientists believe that amino acids “flip” their configuration called an enantiomer (from left-handedness to right-handedness) on exposure to cosmic radiation. This suggests that because proteins show a predisposition to “right-handedness”, the amino acids found in life may have been formed out in space, where they were exposed to cosmic radiation, and then were delivered to Earth via meteorite impacts. All life uses the same 20 amino acids; some bacteria and plants can produce all 20 standard amino acids to make proteins, but animals like humans have to acquire at least 8 of them from eating plants, bacteria, or other animals. Any creature that used a different set of amino acids would be unlike anything on Earth. Amino acids are distinguishable by their chemical R-group, and changing an amino acid R-group completely changes the identity (and chemical properties) of that amino acid. While there are regular 20 amino acids used by life on Earth, researchers have discovered 40 other non-natural amino acids that aren’t used in our biology, but theoretically, they could be used in an alien biochemistry.

Our Areiosan life uses some amino acids recognizable to us, like methionine and cysteine, but their cells also utilize other amino acids like fluoro-tryptophan, which is used in labeling chemicals with a radioactive tracer. Fluoro-tryptophan is similar to our amino acid tryptophan, but the hydrogen R-group has been replaced with a fluorine atom. Areiosian amino acids aren’t right-handed like ours; they are left handed. This suggests that amino acids carried from meteorite collsions which were prodominently right-handed did not play a role in the formation of life on Areios. Amino acids would more likely have come from the abiotic chemistry on the planet’s surface. The genetic material for Areoisan life is right-handed, in contrast to our left-handed DNA. This further isolates our biology because we cannot metabolize anything with right-handed DNA or left-handed amino acids. Mechanically, the shape of those molecules will not function with our metabolism. Add this to the fact that Areiosan life utilizes chemicals like arsenic or fluoride that are deadly to humans and we can reach the conclusion that our two biospheres are all but mutually exclusive. Any life from either biosphere that comes in contact with the other would likely poison each other on contact making any chance for interaction restricted to long-distance communication.

Life from Earth and life from Areios would face a mutual environmental restriction because our metabolisms are so different that we cannot co-mingle.

May 4, 2011

DNA is such a fragile molecule that some researchers don’t think it could have survived in the hydrothermal vents outside of a cell membrane where the earliest life was thought to develop. This is an enigma for researchers studying the origin of life. DNA consists of a double helix molecule that resembles a twisted ladder; the backbone of DNA are linked groups of phosphate chemicals These negatively charged strands run antiparallel to each other, meaning that the top of one strand runs parallel to the bottom of the second strand. Areosian life is truly alien because instead of the familiar phosphate, it uses arsenate ions as a backbone. Arsenate is a polyatomic ion with an arsenic atom in the center and four oxygen atoms bonded to the central arsenic. And Areosian DNA gets weirder still because it is a triple helix.

The ends of a DNA molecule are marked as 3’ (three-prime) on one end and 5’ (five-prime) on the other, so our antiparallel strands link a 3’ to a 5’ end and vice versa. This is important because DNA replication proceeds from an area called the origin of replication on both strands in the 5′-to-3′ direction, forming two replication forks where an enzyme called helicase unzips DNA into two strands. RNA resembles a single strand of DNA, but instead of thymine, RNA exclusively uses the base uracil, which binds to adenine.

In the process of RNA replication called transcription. RNA polymerase unzips a DNA molecule by breaking the hydrogen bonds between complimentary nucleotides. RNA nucleotides are paired with complementary DNA bases. RNA sugar-phosphate backbone forms with assistance from RNA polymerase. Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly synthesized RNA strand. If the cell has a nucleus, the RNA is further processed in a reaction called methylation and then moves through the small nuclear pores to the cytoplasm.

Some scientists speculate that there was a time when life may have used RNA instead of DNA, but there is little evidence to support it. Some have cited that retroviruses based on RNA could indicate that DNA need not have always been the nucleic acid used by life, and that retroviruses may be a throwback from the time when an RNA-World existed. Retroviruses are viruses that run off of RNA-hardware, and Astrobiologist Peter Ward in his book Life As We Do Not Know It, proffers a title for these earlier life forms as members of his proposed kingdom of Ribosa, or RNA-based life.

DNA on Earth uses the same four nucleic acids. And these four nucleic acids come in two categories; pyramidines and purines. Pyramidines are aromatic hydrocarbons like uracil, cytosine and thymine with nitrogen in the 1,3 position of a six-member ring. Purines are organic compounds like adenine and guanine that consist of a pyrimidine ring fused to an alkaloid imidazole ring. Adenine and thymine pair together with 2 hydrogen bonds just like guanine and cytosine pair together with 3 hydrogen bonds. Areosian life uses entirely different purines and pyramidines, but these chemicals function in much the same way as DNA. For instance, Areiosan life features thiopurines, which incorporate sulfur in a purine’s pyramidine ring. Chemicals like mercaptopurine or tioguanine can be found Areiosan cells. Their pyridimine bases incorporate fluorine in their structure, with fluorouracil, floxouridine and gemcitabine as analogues of the purine bases in our cells. These analogues are called antimetabolites because some chemicals like fluorouracil are so chemically similar to uracil that they interfere with our metabolism. These analogues are used in chemotherapy because they interfere with the function of cancer cells. But in Areiosan cells, they function like the real thing and while they may be different from a chemically perspective, they are not fundamentally different in any other way. The machinery inside their cells works just like the machinery in our cells, but the parts are just made of a different material.

RNA synthesis separates the DNA strands and RNA polymerase builds RNA in the 5' to 3' direction, using one of the DNA strands as a template.